1. Field of the Invention
The present invention relates to a device for torque transmission between a pair of rotary members coaxially arranged.
2. Discussion of the Prior Art
This kind of torque transmission device is used as a connection mechanism for effecting torque transmission in response to relative rotation between a pair of rotary shafts coaxially arranged and is also used as a limiting mechanism for limiting difference in rotation between two rotary members. In the former use, the torque transmission device is disposed in a torque transmission system of a four-wheel drive vehicle. In the latter use, the limiting mechanism is disposed in the differential gear unit of a vehicle.
As shown in Japanese Laid-open Patent Publication No. 63-240429, the prior torque transmission device is arranged between a pair of rotary shafts coaxially arranged for relative rotation. The device connects the rotary shafts each other for torque transmission in response to relative rotation therebetween. The device includes a cylindrical housing connected to one of the rotary shafts for rotation therewith, an inner rotary member drivingly connected to the other of the rotary shafts, a multiple friction disc clutch assembled within the housing for effecting torque transmission between the cylindrical housing and the inner rotary member by frictional engagement and a thrust mechanism assembled within the housing for producing a thrust force in accordance with relative rotation between the cylindrical housing and the inner rotary member and applying it to said friction disc clutch.
The thrust mechanism includes an actuation piston which is axially slidably coupled to the cylindrical housing for rotation therewith and forms a clutch chamber receiving the friction disc clutch. The actuation piston is in engagement with the friction disc clutch at one side thereof.
The thrust mechanism also includes a pressure chamber, which is formed at the other side of the actuation piston by the cylindrical housing and the actuation piston. The pressure chamber is filled with an amount of viscous fluid, and a rotor coupled to the inner rotary member in the pressure chamber for rotation therewith, the rotor being integrally formed with a plurality of circumferentially spaced radial blades.
In this kind of torque transmission device, relative rotation between a pair of rotary shafts causes relative rotation between the actuation piston and the rotor. As a result, the viscous fluid in the fluid chamber is compulsorily moved by the blades of the rotor. This produces an internal pressure acting on the actuation piston. Thus, the actuation piston moves toward the friction disc clutch, thereby causing said friction disc clutch to generate an engagement force for effecting drive connection between the rotary shafts. The engagement force is in proportion to the difference in rotation between the rotary shafts and torque in proportion to the difference in rotation is transmitted therebetween.
In the case that said torque transmission device is used in the four-wheel drive vehicle, the driving power is transmitted in accordance with the difference in rotation between front and rear wheels.
In the prior torque transmission device it was impossible to change the characteristic in the torque transmission. However, for the following reason, a new torque transmission device has been desired which can change its transmission characteristic. That to say, it has been hoped to change the distribution ratio of the driving torque to front and rear wheels according to the driving condition of the vehicle. Therefore, the transmission characteristic of the torque transmission device is required to be controllable in accordance with an instruction by the driver or a computer. However, the prior torque transmission device cannot satisfy the above requirement because of its fixed characteristic. The characteristic in the torque transmission is also required to be positively controlled by the computer for eliminating tight-corner braking phenomenon and interference with an antilock braking system.